The invention relates to the field of manufacturing pre-cast concrete panel and joist assemblies used in the construction industry, and more particularly to the field of fabricating such assemblies off site and subsequently transporting the completed assemblies to the construction site for use as load bearing members such as suspended floors or roofs, or of fabricating the assemblies on site where geographically possible. Specifically, the invention relates to the field of fabricating pre-cast concrete and joist assemblies where cambered joists are attached to the concrete panel after the panel has hardened, and to the resulting cambered concrete panel and joist assemblies themselves.
In traditional construction practice, suspended concrete floors in multi-story buildings are formed in place by positioning and bracing the joists to support the floor slab, setting out corrugated decking to receive the wet concrete, placing wire mesh or similar reinforcing materials above the decking, installing edge members to contain the wet concrete, pouring the wet concrete by bucket or pump, allowing the concrete to harden, and removing the extraneous members. Each floor must be fully completed and set up prior to performing any further construction. This method requires specific crews to perform the work, creates situations where mistakes may result in unacceptable and dangerous floor members, and slows construction since the concrete must be allowed to set up over a period of several days.
To alleviate some of these problems, methods have been developed for pre-fabricating the concrete slab and joist assembly. A number of pre-cast concrete panel and joist assemblies can be made and transported to the construction site, ready for installation at the first opportunity. Since the assemblies are pre-cast, construction is not delayed to wait for the setting of the poured concrete. The assemblies are modular in the sense that a number of assemblies are placed in position by crane and then joined together to form a continuous floor assembly.
For example, Cahill in U.S. Pat. No. 973,165 shows a pre-cast concrete slab construction consisting of a reinforced slab formed with concrete ribs on the underside to lighten the weight of the completed slab. The concrete ribs act as modern joist assemblies to handle the compressive load. Longpre et al. in U.S. Pat. No. 4,495,688 teach a method of forming pre-cast concrete panels having joists embedded into the concrete slab. A mold is formed, the concrete is poured in, and pre-constructed joist assemblies are set into the wet concrete to a depth whereby the top chord of the joist is contained within the concrete. It is also known to manufacture joist assemblies such that portions of the webbing material extend beyond the top chord, and this extended webbing is then embedded into the wet concrete, as shown in U.S. Pat. No. 2,558,946 to Fromson.
The method of the invention is distinct and novel from the prior methods since the cambered joist assembly is attached to a flat concrete slab after the slab has hardened. This eliminates having to accurately position the joist member in the wet concrete, thus removing steps from the process, simplifying the level of skill required by the process, and cutting costs and time of manufacture. The method of the invention requires no specially constructed joist assemblies, as standard cambered joists well known in the industry can be used in the process. The method allows cambered joists to be used to produce a cambered slab and joist assembly, without requiring special processing techniques to alter the surface of the hardened concrete slab. The method provides a finished concrete panel and joist assembly having a predetermined amount of camber in both the concrete panel and the joists, even though the slab is initially formed on a flat backer, so that when said assembly is installed the weight of the slab itself and the imposed load removes a portion of the camber, resulting in a positive camber surface on the concrete panel close to planar.